Apparatus including heating source reflective filter for pyrometry

ABSTRACT

Methods and apparatus for processing substrates and measuring the temperature using radiation pyrometry are disclosed. A reflective layer is provided on a window of a processing chamber. A radiation source providing radiation in a first range of wavelengths heats the substrate, the substrate being transparent to radiation in a second range of wavelengths within the first range of wavelengths for a predetermined temperature range. Radiation within the second range of wavelength is reflected by the reflective layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/100,179 filed on Apr. 9, 2008.

TECHNICAL FIELD

This invention relates generally to thermal processing of substrates. Inparticular, specific embodiments of the invention relate to pyrometryduring rapid thermal processing of a semiconductor.

BACKGROUND

Rapid thermal processing (RTP) is a well-developed technology forfabricating semiconductor integrated circuits in which the substrate,for example, a silicon wafer, is irradiated with high-intensity opticalradiation in a RTP chamber to quickly heat the substrate to a relativelyhigh temperature to thermally activate a process in the substrate. Oncethe substrate has been thermally processed, the radiant energy isremoved and the substrate quickly cools. As such, RTP is energyefficient because the chamber surrounding the substrate is not heated tothe elevated temperatures required to process the substrate, and onlythe substrate is heated. In other words, during RTP, the processedsubstrate is not in thermal equilibrium with the surroundingenvironment, namely the chamber.

The fabrication of integrated circuits from silicon or other wafersinvolves many steps of depositing layers, photo lithographicallypatterning the layers, and etching the patterned layers. Ionimplantation is used to dope active regions in the semiconductivesilicon. The fabrication sequence also includes thermal annealing of thewafers for many uses including curing implant damage and activating thedopants, crystallization, thermal oxidation and nitridation,silicidation, chemical vapor deposition, vapor phase doping, thermalcleaning, among others.

Although annealing in early stages of silicon technology typicallyinvolved heating multiple wafers for long periods in an annealing oven,RTP has been increasingly used to satisfy the ever more stringentrequirements for processing substrates with increasingly smaller circuitfeatures. RTP is typically performed in single-wafer chambers byirradiating a wafer with light from an array of high-intensity lampsdirected at the front face of the wafer on which the integrated circuitsare being formed. The radiation is at least partially absorbed by thewafer and quickly heats it to a desired high temperature, for exampleabove 600° C., or in some applications above 1000° C. The radiantheating can be quickly turned on and off to controllably heat the waferover a relatively short period, for example, of one minute or, forexample, 30 seconds, more specifically, 10 seconds, and even morespecifically, one second. Temperature changes in rapid thermalprocessing chambers are capable of occurring at rates of at least about25° C. per second to 50° C. per second and higher, for example at leastabout 100° C. per second or at least about 150° C. per second.

During certain processes, lower temperatures, for example, less thanabout 400° C., may be required. A temperature of a substrate in aprocessing chamber may be below 400° C. and may be as low as about 175°C. An example of such processes is forming silicides on silicon wafers.The quality and performance of processing a substrate such as a siliconwafer in a chamber depends in part on the ability to provide andmaintain an accurate temperature setting of the wafer or substrate.Temperatures of a substrate in a processing chamber are usually measuredby a pyrometer, which measures temperature within a bandwidth ofwavelengths. Radiation which is within the radiation pyrometer bandwidthand which originates from the heating source can interfere with theinterpretation of the pyrometer signal if this radiation is detected bythe pyrometer. To some extent “leaking” heat source radiation caninterfere with the pyrometer reading. In addition, not all wafers areopaque at the pyrometer bandwidth, especially when the wafer is at lowertemperatures. Accordingly, improved systems and methods to measuretemperatures accurately with a pyrometer are required.

SUMMARY

In a first embodiment, a system for processing a substrate, comprises aheat source to provide radiation in a first range of wavelengths; apyrometer to measure the temperature of the substrate when the substratedisposed on a substrate holder within a process area of the chamber bydetecting radiation in a second range of wavelengths within the firstrange of wavelengths; and a window between the heat source and thesubstrate holder, the window being made from a material which issubstantially transparent to radiation in the first range of wavelengthsand having a first reflective coating and a second reflective coating ona surface between the heat source and the substrate holder, thereflective coatings being substantially reflective to radiation in thesecond range of wavelengths, wherein the window is effective to preventradiation within the second range of wavelengths from being transmittedto the pyrometer. In an embodiment, the window is positioned within thechamber to prevent radiation within the second range of wavelengths fromreaching the pyrometer. In one embodiment, the window further comprisingan absorber to absorb radiation in the second range wavelengths.

In certain embodiments, the reflective coatings prevent radiation withinthe second range of wavelength from entering the process area. In one ormore embodiments, the first range of wavelengths is between about400-4000 nm and the second range of wavelengths is between about700-1000 nm and wherein the window having the reflective coatingsprevent radiation from the heat source within the second range ofwavelengths from being transmitted through a substrate at temperaturesbelow about 400° C. In one or more embodiments, the reflective coatingshave a transmittance ratio of reflectance to transmission of light inthe second range of wavelengths of at least 1000.

In specific embodiments, the window comprises a single window elementhaving a first surface and a second surface, the first reflectivecoating being on the first surface of the window and the secondreflective coating being on the second surface of the window. In one ormore embodiments, the absorber comprises a layer of radiation absorbentmaterial. In certain embodiments, the absorber comprises a dopant in thebulk of the window material. The material can be added by doping usingany suitable means such as ion exchange, addition of dopants duringformation of the window material, such as during a chemical vapordeposition process, or any other suitable method.

In specific embodiments, the window comprises a first window element anda second window element spaced from the first window element, and theabsorber comprises a fluid disposed between the first window element andsecond window element. In certain embodiments, the first windowcomprises a top surface facing the heat source and a bottom surface incontact with the fluid and the second window comprises a top surface incontact with the fluid and a bottom surface facing the substrate holder,the first reflective coating being on the bottom surface of the firstwindow element and the second reflective coating being on the bottomsurface of the second window element. In one or more embodiments, thesystem comprises a plurality of windows in a stacked arrangement betweenthe heat source and the substrate holder.

In another embodiment, a system for processing a substrate, comprises: aheat source, the heat source to provide radiation in a first range ofwavelengths; a process area to contain the substrate including asubstrate holder; a first wall of the process area being a windowseparating the heat source from the substrate holder, the window facingand substantially parallel to a first surface of the substrate holder;and a pyrometer directed at a second surface of the substrate holderopposite the first surface to measure the temperature of the substratewhen the substrate is disposed within the process area of the chamber bydetecting radiation in a second range of wavelengths within the firstrange of wavelengths, wherein the window is made from a material whichis substantially transparent to radiation in the first range ofwavelengths, the window having a first reflecting coating and a secondreflecting coating, the reflective coatings being substantiallyreflective to radiation in a second range of wavelengths, the windowfurther comprising an absorber to absorb radiation in the second rangewavelengths.

In specific embodiments, the window is effective to prevent radiationfrom the heat source within the second range of wavelengths from beingtransmitted through a substrate comprising silicon and being measured bythe pyrometer at temperatures below about 400° C.

In other aspects of the invention, methods of processing substrates areprovided in which a substrate is thermally processed in systems of thetype described herein, and one or more windows containing reflectivecoatings are disposed between the heat source and the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross-sectional view of a rapid thermal processingchamber according to one or more embodiments;

FIG. 2 shows another cross-sectional view of a rapid thermal processingchamber according to one or more embodiments;

FIGS. 3A and 3B shows graphs of filter transmission versus wavelength inaccordance with an aspect of the present invention;

FIG. 4 shows a cross-sectional view of a heat source in accordance withan aspect of the present invention;

FIG. 5A is a schematic partial cross-sectional view processing chamberin accordance with one embodiment of the present invention;

FIG. 5B is a schematic partial cross-sectional view processing chamberin accordance with one embodiment of the present invention;

FIG. 6 is a schematic partial cross-sectional view processing chamber inaccordance with one embodiment of the present invention; and

FIG. 7 shows two graphs of radiation filter characteristics inaccordance with an aspect of the present invention.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways.

According to one or more embodiments of the invention, a thermalprocessing chamber for processing a substrate such as a semiconductorwafer is provided. Wafer temperature is measured by radiation pyrometry.Wafer temperature can be determined through radiation pyrometry bydetermining the emissivity of the substrate and applying known radiationlaws to calibrate a pyrometer for accurate temperature measurements.Radiation within the bandwidth or wavelength range of the pyrometerwhich originates from the heating source (e.g., the lamps) interfereswith the interpretation of the pyrometer signal if this radiation isdetected by the pyrometer. This may be due to leakage of sourceradiation in the chamber that reaches the pyrometer, or source radiationthat reaches the pyrometer when the wafer is “transparent” to sourceradiation. This may occur, for example with silicon wafers duringoperation of the chamber at temperatures below 450° C., and as low as150° C.

FIG. 1 schematically represents a rapid thermal processing chamber 10.Peuse et al. describe further details of this type of reactor and itsinstrumentation in U.S. Pat. Nos. 5,848,842 and 6,179,466. A wafer 12,for example, a semiconductor wafer such as a silicon wafer to bethermally processed is passed through the valve or access port 13 intothe process area 18 of the chamber 10. The wafer 12 is supported on itsperiphery by a substrate support shown in this embodiment as an annularedge ring 14 having an annular sloping shelf 15 contacting the corner ofthe wafer 12. Ballance et al. more completely describe the edge ring andits support function in U.S. Pat. No. 6,395,363. The wafer is orientedsuch that processed features 16 already formed in a front surface of thewafer 12 face upwardly, referenced to the downward gravitational field,toward a process area 18 defined on its upper side by a transparentquartz window 20. Contrary to the schematic illustration, the features16 for the most part do not project substantial distances beyond thesurface of the wafer 12 but constitute patterning within and near theplane of the surface. Three lift pins 22 may be raised and lowered tosupport the back side of the wafer 12 when the wafer is handed between apaddle or robot blade (not shown) bringing the wafer into the chamberand onto the edge ring 14. A radiant heating apparatus 24 is positionedabove the window 20 to direct radiant energy toward the wafer 12 andthus to heat it. In the reactor 10, the radiant heating apparatusincludes a large number, 409 being an exemplary number, ofhigh-intensity tungsten-halogen lamps 26 positioned in respectivereflective tubes 27 arranged in a hexagonal close-packed array above thewindow 20. The array of lamps 26 is sometimes referred to as thelamphead. However, other radiant heating apparatus may be substituted.Generally, these involve resistive heating to quickly ramp up thetemperature of the radiant source. Examples of suitable lamps includemercury vapor lamps having an envelope of glass or silica surrounding afilament and flash lamps which comprise an envelope of glass or silicasurrounding a gas such as xenon, which provides a heat source when thegas is energized. As used herein, the term lamp is intended to coverlamps including an envelope that surrounds a heat source. The “heatsource” of a lamp refers to a material or element that can increase thetemperature of the substrate, for example, a filament or gas that can beenergized.

As used herein, rapid thermal processing or RTP refers an apparatus or aprocess capable of uniformly heating a wafer at rates of about 50°C./second and higher, for example, at rates of 100° to 150° C./second,and 200° to 400° C./second. Typical ramp-down (cooling) rates in RTPchambers are in the range of 80-150° C./second. Some processes performedin RTP chambers require variations in temperature across the substrateof less than a few degrees Celsius. Thus, an RTP chamber must include alamp or other suitable heating system and heating system control capableof heating at rate of up to 100° to 150° C./second, and 200° to 400°C./second distinguishing rapid thermal processing chambers from othertypes of thermal chambers that do not have a heating system and heatingcontrol system capable of rapidly heating at these rates.

In accordance with a further aspect of the present invention embodimentsof the present invention may be applied also to flash annealing. As usedherein flash annealing refers to annealing a sample in less than 5seconds, specifically, less than 1 second, and in some embodiments,milliseconds.

It is important to control the temperature across the wafer 12 to aclosely defined temperature uniform across the wafer 12. One passivemeans of improving the uniformity includes a reflector 28 extendingparallel to and over an area greater than the wafer 12 and facing theback side of the wafer 12. The reflector 28 efficiently reflects heatradiation emitted from the wafer 12 back toward the wafer 12. Thespacing between the wafer 12 and the reflector 28 is preferably withinthe range of 3 to 9 mm, and the aspect ratio of the width to thethickness of the cavity is advantageously greater than 20. In accordancewith one aspect of the present invention a reflector plate is applied toenhance the apparent emissivity of a substrate such as a wafer. Thereflector 28, which may be formed of a gold coating or multi-layerdielectric interference mirror, effectively forms a black-body cavity atthe back of the wafer 12 that tends to distribute heat from warmerportions of the wafer 12 to cooler portions. In other embodiments, forexample, as disclosed in U.S. Pat. Nos. 6,839,507 and 7,041,931, bothincorporated herein by reference in their entireties, the reflector 28may have a more irregular surface or have a black or other coloredsurface to more closely resemble a black-body wall. The black-bodycavity is filled with a distribution, usually described in terms of aPlanck distribution, of radiation corresponding to the temperature ofthe wafer 12 while the radiation from the lamps 26 has a distributioncorresponding to the much higher temperature of the lamps 26.Preferably, the reflector 28 is deposited on a water-cooled base 53preferably made of metal to heat sink excess radiation from the wafer,especially during cool down. Accordingly, the process area of theprocessing chamber has at least two substantially parallel walls, ofwhich a first is a window 20, preferably made of a material beingtransparent to radiation such as quartz, and a second wall 53substantially parallel to the first wall which is preferably made ofmetal and is significantly not transparent.

One way of improving the uniformity includes supporting the edge ring 14on a rotatable cylinder 30 that is magnetically coupled to a rotatableflange 32 positioned outside the chamber. A motor (not shown) rotatesthe flange 32 and hence rotates the wafer about its center 34, which isalso the centerline of the generally symmetric chamber.

Another way of improving the uniformity divides the lamps 26 into zonesarranged generally ring-like about the central axis 34. Controlcircuitry varies the voltage delivered to the lamps 26 in the differentzones to thereby tailor the radial distribution of radiant energy.Dynamic control of the zoned heating is affected by, one or a pluralityof pyrometers 40 coupled through one or more optical light pipes 42positioned to face the back side of the wafer 12 through apertures inthe reflector 28 to measure the temperature across a radius of therotating wafer 12. The light pipes 42 may be formed of variousstructures including sapphire, metal, and silica fiber. A computerizedcontroller 44 receives the outputs of the pyrometers 40 and accordinglycontrols the voltages supplied to the different rings of lamps 26 tothereby dynamically control the radiant heating intensity and patternduring the processing. Pyrometers generally measure light intensity in anarrow wavelength bandwidth of, for example, 40 nm in a range betweenabout 700 to 1000 nm. The controller 44 or other instrumentationconverts the light intensity to a temperature through the well knownPlanck distribution of the spectral distribution of light intensityradiating from a black-body held at that temperature. Pyrometry,however, is affected by the emissivity of the portion of the wafer 12being scanned. Emissivity ∈ can vary between 1 for a black body to 0 fora perfect reflector and thus is an inverse measure of the reflectivityR=1−∈ of the wafer back side. While the back surface of a wafer istypically uniform so that uniform emissivity is expected, the backsidecomposition may vary depending upon prior processing. The pyrometry canbe improved by further including a emissometer to optically probe thewafer to measure the emissivity or reflectance of the portion of thewafer it is facing in the relevant wavelength range and the controlalgorithm within the controller 44 to include the measured emissivity.

In the embodiment shown in FIG. 1, the separation between the substrate12 and the reflector 28 is dependent on the desired heat flow for thegiven substrate 12. In one embodiment, the substrate 12 can be disposedat a greater distance from the reflector 28 to decrease the heat flow tothe substrate. In another embodiment, the substrate 12 can be placedcloser to the reflector 28 to increase the heat flow to the substrate12. The exact position of the substrate 12 during the heating of thesubstrate 12 and the residence time spent in a specific position dependson the desired amount of heat flow to the substrate 12.

In another embodiment, when the substrate 12 is in a lower position,proximate the reflector 28, the thermal conduction from the substrate 12to the reflector 28 increases and enhances the cooling process. Theincreased rate of cooling in turn promotes optimal RTP performances. Thecloser the substrate 12 is positioned to the reflector 28; the amount ofthermal exposure will proportionally decrease. The embodiment shown inFIG. 1 allows the substrate 12 support to be easily levitated atdifferent vertical positions inside the chamber to permit control of thesubstrate's thermal exposure. It will be understood that theconfiguration shown in FIG. 1 is not intended to be limiting. Inparticular, the invention is not limited to configurations in which theheat source or lamps are directed at one side or surface of thesubstrate and the pyrometers are directed at the opposite side of thewafer.

As noted above, wafer temperature in the process area of a processingchamber is commonly measured by radiation pyrometry. While radiationpyrometry can be highly accurate, radiation which is within theradiation pyrometer bandwidth and which originates from the heatingsource may interfere with the interpretation of the pyrometer signal ifthis radiation is detected by the pyrometer. In Applied Materials' RTPsystems this minimized by the process kit and by the wafer itself. Theprocess kit couples the wafer with the rotation system. It may include asupport cylinder which is shown as 30 in FIG. 1. It may also include asupport ring which is not shown in the Figures but it may be used incertain processing chamber configurations). Such a support ring isbasically an auxiliary edge ring which supports the edge ring, which isshown as 14 in FIG. 1.

In general, one or more pyrometers 40 as shown in FIG. 1 may bepositioned in such a way that the substrate or wafer 12 shields theradiation source 26 from the pyrometer. A substrate such as a wafer islargely transparent to radiation for wavelengths greater than or about1100 nm. Accordingly, one way to limit heat source radiation fromreaching the pyrometer is to measure radiation at wavelengths at whichthe substrate may be substantially opaque to the wavelength. For asilicon wafer, such wavelengths may be at about 1100 nm and lower.Nevertheless, as noted above, the process kits can “leak” sourceradiation and not all wafers are opaque at the pyrometer bandwidth,especially when the wafer is at lower temperatures, of about 450° C. andlower. In a further embodiment the temperature may be about 400° C. andlower. In yet a further embodiment the temperature may be about 250° C.and lower. In a further embodiment the temperature may be high and maybe above the melting point of the substrate such as a wafer that isbeing processed in the chamber.

In accordance with an embodiment of the present invention, one solutionto the radiation originating from the heating source either by “leaking”or by transmitting through the substrate is to prevent the sourceradiation in the pyrometer bandwidth from reaching to the wafer. Inaccordance with a further aspect of the present invention, the radiationin the pyrometer bandwidth is reflected back to the source. This may bedone by coating the window 20 in FIG. 1 that is separating the heatsource from the process atmosphere 18 with a material 51 which reflectsthe pyrometer bandwidth radiation while permitting sufficient sourceradiation for heating to pass through the window 20. A film ofreflective coating 50 may be placed on the side of the window facing theheat source as is shown in FIG. 1. In another embodiment, a reflectivelayer 51 may be placed on the side of the window 20 facing the substrateas is shown in FIG. 2. In another embodiment, a reflective layer may beapplied to both sides of the window. In a specific embodiment, theentire window 20 is covered completely with a reflective layer, andthere is no gap or opening in the coating. In other words, the window 20comprising a reflective layer with no interruption in the reflectivelayer or the window 20 separates the substrate from the heat source.There is no transparent segment in the window 20 that disrupts or breaksthe continuous reflective layer on the window 20.

By covering the window 20 with a reflective coating in a range ofwavelengths at which a pyrometer is sensitive, substantially noradiation in that range of wavelengths coming directly from the heatsource will reach the pyrometer. Accordingly, when the pyrometer detectsradiation in the range of wavelengths it is radiation coming only orsubstantially only from the substrate, even when the substrate istransparent to that range of wavelengths, for example, for a siliconwafer being processed at temperatures below about 400° C., and morespecifically, below about 250° C. The use of the reflective layerimproves the accuracy of the pyrometer.

In one embodiment, the window 20 can be removed from the chamber and becoated by one or more layers of reflective layer. The reflectivebehavior of the film depends on selected materials, number of layers andthickness of the layers. Processes and providers of services to providewindows with thin layers of reflective layer for reflection in specifiedrange of wavelengths are known. One provider of such coating services isfor instance JDS Uniphase. Materials that can be used in a reflectivelayer in an embodiment of the film may be alternating layers of, ingeneral, any combination of high index and low index dielectricmaterials which are substantially transparent to most of the radiationemitted from the heating source, such as titania-silica ortantala-silica. In one embodiment, the reflective layer is made up ofSiO₂ and Ta₂O₅ layers. In a specific embodiment, the outermost layercomprises SiO₂.

In one embodiment, the layers may include multiple (thin) layers ofoptically transparent materials with different refractive indices, whichare sometimes referred to as dielectric mirrors. The layers may bedeposited on a substrate such as a window 20. A multilayer dielectricmirror may work as a reflective filter, wherein radiation is reflected.Radiation may be reflected selectively dependent among other elements onthe wavelength of the radiation, the angle of incidence of theradiation, properties of the applied dielectric material including therefractive index of the applied dielectric material, the thickness ofeach layer, the number of layers a different thickness, and arrangementof layers. The filter properties of a multilayer dielectric mirror maybe illustrated by a graph as provided in graph 300 of FIG. 3A. Such agraph shows a transmittance of reflected radiation in percentagerelative to the provided radiance dependent on wavelength of radiation.As seen in FIG. 3A, within a range of about 700 nm to 1200 nm noradiation is reflected, while for instance well above 1200 nm more than95% of the radiation is reflected. This filter as illustrated in FIG. 3Amay be characterized as a band-stop filter or a notch filter.

In a specific embodiment, only the window 20 as part of the process areahas to be coated. Furthermore, in a specific embodiment, the window iscoated completely with no openings in the layer. In one or moreembodiments, the window 20 is removable. This makes servicing of thecoating for repair or re-application of the film or exchange of thewindow with a replacement window relatively easy to do. In specificembodiments, the wall 53 is not coated.

In accordance with a further aspect of the present invention, apyrometer will be used to measure relatively low temperatures belowabout 400° C. or below about 250° C. to about 175° C. by detectingradiation with the pyrometer in a range of wavelengths of about 700-1100nm. The range of wavelengths radiated by a heat source in a processingchamber usually ranges from below 700 nm to above 5.5 micron. Materialssuch as quartz become opaque at wavelengths above 5.5 micron. Whenradiation with wavelengths between about 700-1100 nm is reflected backto the heat source sufficient radiation of other wavelengths will stillbe available from the source to heat the substrate to temperatures belowabout 400° C.

In one embodiment, the reflective layer is a broad band reflectivefilter. In one embodiment, it operates as a reflective filter with amaximum reflective ratio of about 100% or with a maximum reflection totransmission ratio of about not less than 1000 in a range of 700 nm-1100nm. A relative bandwidth is defined herein as

${bw}_{rel} = \frac{\lambda_{high} - \lambda_{low}}{\lambda_{center}}$with λ_(center) being the wavelength at the arithmetical average ofλ_(high) and λ_(low). Herein the λ_(low) is determined as the wavelengthwhere above the measured reflection is 50% of the measured incidentradiation and λ_(high) is determined as the wavelength where below themeasured reflection is 50% of the measured incident radiation.

This aspect is illustrated in FIGS. 3A and 3B, which show a modeledtransmittance characteristic of a filter in accordance with an aspect ofthe present invention. FIG. 3A shows transmittance on a linear scale asa function of wavelength. FIG. 3B shows transmittance on a logarithmicscale. Arrow 303 in both graphs identifies the 50% point for determiningthe relative bandwidth of this filter. The relative bandwidth of thisfilter is about 50%.

In one embodiment of the present invention, in a range of 700 nm-1100nm, the relative bandwidth of the reflective layer is about 44%. In afurther embodiment, the range of reflective wavelengths is about700-1000 nm, which provides a relative bandwidth of the reflective layerof about 35%. A relative bandwidth of about 30% or higher is definedherein as a broad band, while a relative band of about lower than 30%will be defined as a narrow band. Accordingly, the bandwidth of thefilter of FIGS. 3A and 3B is a broad band.

The reflective properties of a multi-layer reflective layer depend onthe wavelength of the radiation. The ratio of reflection to transmissionalso depends on the Angle of Incidence (AOI) from a source to thesurface of the film. In one embodiment, a reflective layer is designedfor reflection to transmission ratio based on radiation leaving a lampwith an AOI not greater than 45°.

In one embodiment, a filter which passes most source radiation andreflects the pyrometer bandwidth radiation is placed on either theoutside or inside or on both surfaces of a window separating a heatingsource from the process chamber has been provided above. As used herein,the term “window” refers to material between the substrate and the heatsource. In embodiments in which the heat source is a lamp, the termwindow is intended to include the lamp envelope which is typically madefrom quartz or any other suitable material.

Thus, in a further embodiment, the filter may also be placed on theinner or outer surface of an envelope of a radiation source or on bothsurfaces. An illustration of this aspect is shown in FIG. 4 with a layer401 external to an enveloped 402 on a lamp 400. This has as an addedbenefit that it may raise the efficiency of the heat source.

In a further embodiment, the performance of a pyrometer in a designatedrange of wavelengths may be improved by adding an absorber material tothe reflective layer, preferably in a layer between two reflectinglayers of the film. The absorber may also be part of the substrate towhich a reflective layer is applied, in the form of a dopant or addedmaterial. Thus, the substrate to which the layer is applied may bepartly absorptive. The substrate to which the reflective layer isapplied may also be doped with a material that enhances absorptiveproperties of the substrate. The substrate with the reflective layerpreferably is a window such as window 20 in FIGS. 1 and 2. In otherembodiments, an absorbing fluid may be provided between a pair of windowpanes. The absorber does have to absorb somewhat in the pyrometerbandwidth, but can absorb in other spectral regions though preferablynot so much in the radiation source region. Since the two reflectingfilms, either on opposite sides of a single windows or on two separatewindows in a spaced apart relationship can act as a hall of mirrors forthe pyrometer bandwidth, the net effect of the absorption will bemagnified. Any material absorbing radiation in the pyrometer bandwidth,to an amount of some but less than a few % over the radiation spectrumpassing through quartz (˜0.4 to 4 microns), will be suitable. In oneembodiment, rare earth oxides are an excellent candidate for being addedas an absorber material to the reflective layer or substrate. In afurther embodiment, a band pass absorber (such as Si) that passes moresource radiation than pyrometer radiation may be added to the layer orsubstrate. In yet a further embodiment, a general absorptive materialmay be added to the layer, for example, carbon, metals, other oxidesmiscible with the layer materials or window (substrate) material. Windowmaterials may include quartz, alumina, yttria, glasses, or othersubstantially transparent ceramics.

FIGS. 5A and 5B schematically illustrate the concept of adding anabsorber material to a filter. As shown in FIG. 5A, chamber 500 includesa heat source 502, which may be a lamphead, and a window 508 having afirst or top surface facing the heat source 502 and a second or bottomsurface facing a wafer 512 that is heated by radiation through aradiation path illustrated by arrows 504. As noted above, one or tworeflective coatings, which may be dielectric multilayer filters, can beprovided on the window 508, each of which reflects radiation in a bandof radiation wavelengths in which a pyrometer is operational. This typeof filter arrangement can be described as a “notch filter”, wherein anotch indicates a reflection band. In a first embodiment, a firstreflective coating in the form of a dielectric multilayer notch filter506 can be disposed on only the top surface of the window 508. Thismultilayer notch filter 506 may be referred to as a “top filter stack”,wherein the stack is formed by a plurality of dielectric layers. Theposition “top” is defined by the fact that the filter is on the windowside that is the farthest away from the wafer 512. In a secondembodiment, a second reflective coating in the form of a dielectricmultilayer notch filter 510 is disposed on only the bottom surface ofthe window 508. This multilayer notch filter 510 may be referred to as a“bottom filter stack”, wherein the stack is formed by a plurality ofdielectric layers. The position “bottom” is defined by the fact that thefilter is on the window side that is the closest to the wafer 512. Inthe embodiment shown in FIG. 5A, both a top filter stack 506 and abottom filter stack 508 are applied to window 508.

As discussed above, the single dielectric multilayer filter or the dualdielectric multilayer filters are applied to prevent radiation in aselected wavelength range as generated by the heat source, from enteringthe processing chamber where the wafer 512 is being processed. Thisassures that radiation in the selected range that is detected by apyrometer, such as a pyrometer 40 in FIG. 1, most likely is radiationgenerated by the wafer. This can be achieved by using either a singlenotch filter or dual notch filters having a reflecting notch that coversthe complete reflection range.

In one or more embodiment, dual filters such as top filter 506 andbottom filter 510 may have overlapping or additive reflective ranges. Anexample of such an overlapping arrangement is illustrated in FIG. 7, inwhich 701 shows an approximation of a transmittance characteristic as afunction of wavelength of a first filter. This filter, as indicated by701, completely or almost completely passes radiation in a range ofwavelengths smaller than λ₂ and greater than λ₃. It completely, oralmost completely, reflects radiation in a wavelength range between λ₂and λ₃. A second filter represented by 702 reflects radiation completelyor almost completely in a wavelength range between λ₁ and λ₄, whereinλ₁<λ₂<λ₄,<λ₃. As a consequence, the use of the two filters havingcharacteristics as shown in 701 and 602 on top and bottom of the windowwill create a combined reflection of radiation in a range of λ₁,-λ₃.Accordingly, substantially no or only a limited amount of radiation in awavelength range of λ₁,-λ₃ generated by the lamphead will reach thewafer, when two filters with the complementary notches are used. Usingsuch a complementary approach may be advantageous for creating theindividual filters and may provide a better overall filtercharacteristic.

As discussed above, if the dielectric multilayer mirrors are applied onboth sides of the window, this may create a “hall of mirrors” effect.With respect to FIG. 5A, the “hall of mirrors” effect may occur for topand bottom filter 506 and 510 having the same reflective wavelengthrange, or when the two filters have a substantial overlap in reflectivewavelength range. Minimizing overlap in reflective wavelength range iftwo filters 506 and 510 are used may minimize the “hall of mirrors”effect. A “hall of mirrors” effect captures radiation energy ofradiation in the reflective wavelength range of the filters between themirrors inside the window, which may be undesirable. As discussed above,a radiation absorbing material may be included in the window that atleast absorbs radiation energy in the reflective wavelength range of thedielectric mirrors. A material that absorbs radiation in a broad rangeof wavelengths or a material that absorbs in a limited range such as thereflective wavelength range can be used. In one embodiment, in using abroad range absorbing material, enough absorbent material is used tosufficiently dampen the “hall of mirrors” effect in the reflectivewavelength range, without substantially affecting the energy transferfrom lamphead to processing chamber in the non-reflecting range. In yeta further embodiment, the window material, which may be quartz, can bedoped with an absorbing material. This is illustrated as dashed lines516 in FIG. 5A. To limit broadband energy loss as well as prevent theoverheating of the window the concentration of absorbing material in thewindow can be limited to less than about 5% by weight, or in morespecific embodiments, less than about 1% by weight or less.

In yet a further embodiment illustrated in FIG. 5B, one or more layersof absorbing material at least including the reflective wavelength rangeof the filters on one side on or both sides of the window can beprovided. This is illustrated in FIG. 5B as 514 and 518. The purpose ofthe absorbing layer is to dampen reflected radiation. For that reason,absorbing layers 514 and 518 should be located between reflectivecoatings 506 and 510 and the bulk of the window material. An absorbinglayer may be a layer such as a film layer that is deposited on thewindow before the reflective dielectric layers are deposited.

In yet a further embodiment an absorbing layer may be part of a dopinglayer of the quartz window. Such a layer may also be a gradient layer.Accordingly, radiation in the reflective wavelength range coming fromthe window before it enters the dielectric stack will be attenuatedbefore it is reflected back and will be attenuated again afterreflection before it re-enters the window.

In another embodiment, a plurality of windows can be arranged in astacked relationship between the heat source and the substrate. Thus twoor more windows can be arranged, each of the windows having one or morereflective coatings. One or more of the windows 508 can have an absorberas described in FIGS. 5A and 5B above, or as described below withrespect to FIG. 6. Windows of different types, for example one or moreof each type of window in FIG. 5A, FIG. 5B, and/or FIG. 6 can bearranged in a stacked relationship between the heat source and thesubstrate. The windows can be arranged in a spaced apart relationship,or they can be abutting each other.

In a further embodiment shown in FIG. 6, a window such as the window 20of FIGS. 1 and 2 may be a composite window 618 comprising two windowelements 608 and 609, which may be provided with a gap between thewindows. The window is disposed between heat source 602 and substrate612 that is heated by radiation through a radiation path illustrated byarrows 604. According to one or more embodiments, both window elements608 and 609 in the composite window 618 are transparent to a broad rangeof radiation, except for a first wavelength band of radiation inside thebroad range for which the window is absorptive. This can be achieved bydoping a window with low levels of an absorber. The outside surfaces(where “inside” is defined as between the two windows) coated withreflective coatings 606 and 611 which is reflective to substantiallyradiation in the first wavelength band of radiation. In alternativeembodiments, the reflective coatings 606 and 611 may be applied to theinside surfaces instead of or in addition to being applied to theoutside surfaces. In this embodiment, as the light passes through thefirst outside coating 606, it passes through the first window 608 of thecomposite window, a gap, the second window 609 of the composite window,reflect off of the second window's coating 611, pass back through thesecond window, the gap, and back through the first window again, etc.This configuration maximizes the number of times light would have topass through a window (with absorber) per reflection—2 passes per onereflection—and in turn minimizes the amount of absorber that is needed.Accordingly, the gap between the windows 606 and 609 can be filled witha light absorbing fluid 614, which may be gas or liquid. The fluid 614may also provide cooling of the composite window 618. If additionalabsorbance is desired absorber 616 may be doped in window 608 and/orabsorber 619 can be doped in window 609. The fluid 614 may be providedinto the gap by a system that may include a pump that pumps the liquidor gas through the gap. The system may also have a temperature controlsystem that controls the temperature of the liquid or gas and thus mayserve to control the temperature of the window. Absorbing material maybe added to the gas or liquid to diminish the “hall of mirrors” effect.These absorbing materials can be a rare earth materials or any othersuitable absorbing material.

In a further embodiment one may apply a composite window that containsat least two windows, wherein each side of each window is provided witha multi-layer dielectric reflective filter with a unique range ofreflective wavelengths. In such a composite window, the total filtercharacteristic is then provided by the summation of up to fourindividual filter characteristics of each stack of dielectric layers. Ifa composite window comprises more than two individual windows, the totalfilter characteristic may be formed from individual filters, eachcreated on a side of a window.

As yet a further embodiment of a composite window, comprising at least afirst and a second window, a first outside window may be a transparentwindow. A second window with a reflective coating may be positionedbetween the process area and the first window. The first window mayprovide protection of chemical and/or mechanical wear of the secondwindow and/or its coating.

It will be understood that in the figures, the heat source is positionedabove the substrate and the pyrometer is placed below the heat source.Other configurations of the processing chamber are possible and arefully contemplated and within the scope of this invention. For instance,a processing chamber may have a heating source below a substrate and apyrometer positioned above a heat source. These and other variations ofpositioning of substrate, heat source and pyrometer in a processingchamber are possible and contemplated without fundamentally affectingaspects of the inventions described herein.

In a further embodiment, a second wall 53, as shown in FIGS. 1 and 2,may comprise a window that is transparent to radiation instead of ametal wall. Such a second window is preferably substantially transparentto heating radiation, which may be provided by a second lamphead whichhas a similar function as lamphead 24 in FIGS. 1 and 2. The secondwindow being substantially parallel to a substrate such as a wafer andwhich separates the process area from the second lamphead. Accordingly,in such a configuration the substrate such as a wafer can be heated fromat least two sides. The second window in yet another embodiment may havea reflective layer, which may be in one of the configurations orembodiments of the first window. In an embodiment that includes twowindows with two lampheads, thus exposing a substrate such as a wafer toradiation at two surfaces, the set-up of the pyrometer may also bemodified. In a further embodiment, a pyrometer can be located in or onor behind a wall that is substantially perpendicular to a window with areflective layer as was disclosed earlier. In that case the pyrometer islooking at a substrate such as a wafer from a side, rather than fromabove or below. In order to capture sufficient radiation from asubstrate one can use several embodiments of positioning a pyrometer. Ina further embodiment the pyrometer may be positioned in or behind anopening of a side wall located in a plane parallel to the substrate suchas a wafer, the plane being higher or lower than the level of thesubstrate. This allows the pyrometer to look at the substrate under anangle, thus allowing capturing sufficient radiation from a surface ofthe substrate. In a further embodiment, a light pipe, such as a quartztube, may be inserted through a hole in a side wall from into theprocess area of the chamber. The hole being in a plane parallel to thesubstrate and the plane being above or below the plane of the substrate.A light pipe may be arranged in such a way that the end of the lightpipe in the process area is parallel to a surface of the substrate. Inanother embodiment of the light pipe, the light pipe may be entering theprocess area parallel to a surface of the substrate such as a wafer. Thelight pipe can be provided with a bend at the side inside the processchamber so that it is substantially perpendicular to and above or belowthe surface of the substrate.

In yet a further embodiment, in embodiments having two windows with twolampheads or heating sources, both windows may be doped with an absorberand coated with a reflective coating. In yet a further embodiment of achamber having two windows and two lampheads or heating sources, eachwindow may be a composite window as described above.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. For example, while the embodiments described abovewith respect to FIG. 1 and FIG. 2 were described to rapid thermalprocessing chambers, it will be understood that the principles of thepresent invention can be applied to a variety of thermal processingchambers and the present invention is not limited to rapid thermalprocessing. It will be apparent to those skilled in the art that variousmodifications and variations can be made to the method and apparatus ofthe present invention without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention includemodifications and variations that are within the scope of the appendedclaims and their equivalents.

1. A system for processing a substrate, comprising: a heat source toprovide radiation in a first range of wavelengths; a pyrometer tomeasure the temperature of the substrate when the substrate is disposedon a substrate holder within a process area of the chamber by detectingradiation in a second range of wavelengths within the first range ofwavelengths; and a window between the heat source and the substrateholder, the window being made from a material which is transparent toradiation in the first range of wavelengths and having a firstreflective coating and a second reflective coating on a surface betweenthe heat source and the substrate holder, the reflective coatings beingreflective to radiation in the second range of wavelengths, wherein thewindow is effective to prevent radiation within the second range ofwavelengths from being transmitted to the pyrometer, wherein the windowcomprises a first window element having a first surface facing the heatsource and a second surface facing the substrate holder and one of thefirst reflective coating and the second reflecting coating is on thefirst surface and the first reflective coating and the second reflectivecoating having a range of reflective wavelengths that overlap.
 2. Thesystem of claim 1, wherein the window is positioned within the chamberto prevent radiation within the second range of wavelengths fromreaching the pyrometer.
 3. The system of claim 1, the window furthercomprises an absorber to absorb radiation in the second range ofwavelengths.
 4. The system of claim 2, wherein the reflective coatingsprevent radiation within the second range of wavelengths from enteringthe process area.
 5. The system of claim 1, wherein the first range ofwavelengths is between about 400-4000 nm and the second range ofwavelengths is between about 700-1000 nm and wherein the window havingthe reflective coatings prevent radiation from the heat source withinthe second range of wavelengths from being transmitted through asubstrate at temperatures below about 400° C.
 6. The system of claim 5,wherein the reflective coatings have a transmittance ratio ofreflectance to transmission of light in the second range of wavelengthsof at least
 1000. 7. The system of claim 3, wherein the window comprisesa single window element having the first surface and a second surface,the first reflective coating being on the first surface of the windowand the second reflective coating being on the second surface of thewindow.
 8. The system of claim 7, wherein the absorber comprises a layerof radiation absorbent material.
 9. The system of claim 7, wherein theabsorber comprises a dopant in the window material.
 10. The system ofclaim 3, wherein the window comprises a first window element and asecond window element spaced from the first window element, and theabsorber comprises a fluid disposed between the first window element andsecond window element.
 11. The system of claim 10, wherein the firstwindow comprises a top surface facing the heat source and a bottomsurface in contact with the fluid and the second window comprises a topsurface in contact with the fluid and a bottom surface facing thesubstrate holder, the first reflective coating being on the bottomsurface of the first window element and the second reflective coatingbeing on the bottom surface of the second window element.
 12. The systemof claim 1, wherein the system comprises a plurality of windows in astacked arrangement between the heat source and the substrate holder.13. A system for processing a substrate, comprising: a heat source, theheat source to provide radiation in a first range of wavelengths; aprocess area to contain the substrate including a substrate holder; afirst wall of the process area being a window separating the heat sourcefrom the substrate holder, the window facing and substantially parallelto a first surface of the substrate holder; and a pyrometer directed ata second surface of the substrate holder opposite the first surface tomeasure the temperature of the substrate when the substrate is disposedwithin the process area of the chamber by detecting radiation in asecond range of wavelengths within the first range of wavelengths,wherein the window is made from a material which is transparent toradiation in the first range of wavelengths, the window having a firstreflective coating on a first surface of the window facing the heatsource and a second reflective coating, the reflective coatings beingsubstantially reflective to radiation in a second range of wavelengths,and the first reflective coating and the second reflective coatinghaving a range of reflective wavelengths that overlap the window furthercomprising an absorber to absorb radiation in the second rangewavelengths.
 14. The system of claim 13, wherein the window is effectiveto prevent radiation from the heat source within the second range ofwavelengths from being transmitted through a substrate comprisingsilicon and being measured by the pyrometer at temperatures below about400° C.
 15. The system of claim 14, wherein the second range ofwavelengths is between about 700-1000 nm.
 16. The system of claim 15,wherein the first and second reflective coatings have a transmittanceratio of reflectance to transmission of light in the second range ofwavelengths of at least
 1000. 17. The system of claim 13, wherein thewindow comprises a pair of window elements in a spaced apartrelationship, one window element having the first reflective coating ona surface of the window facing the heat source and the other windowelement having the second reflective coating on a surface of the windowfacing the heat source, the absorber comprising a fluid between the pairof window elements.
 18. The system of claim 13, wherein the windowcomprises quartz and the absorber comprises a dopant in the quartz. 19.The system of claim 14, wherein the first coating and the second coatingeach comprise multiple layers.
 20. The system of claim 13, wherein theabsorber comprises a layer of absorbent material.